Under the enforcement of stringent regulations to preserve environment, airlines encounter increasing financial burden particularly in paying pollution fines. This could be avoided if airlines could improve their environmental (green) performance. This paper proposes a novel methodology to quantify airline’s green performance. A ‘Green Fleet Index (GFI)’ framework is formulated by capturing three major environmental factors, namely aircraft emission, noise and fuel efficiency. The proposed framework also allows the evaluation of various improvement strategies to yield a greener performance. A realistic case study, with 38 international routes, is presented to examine the applicability of the developed framework. The findings show that aircraft emission, noise and fuel efficiency could affect the green performance of airlines to a great extent. Furthermore, the results point out the effectiveness of a particular mitigation strategy that performs differently on specific environmental factors (emission, noise and fuel efficiency). It is anticipated that this study may reveal some beneficial insights for airlines to operate in a sustainable and environmental manner, which would benefit air travellers as well as the community in return.